U.S. patent number 4,474,585 [Application Number 06/499,688] was granted by the patent office on 1984-10-02 for synthetic yarn-reinforced flexible webs stabilized against elongation, coated abrasive thereon, and process therefor.
This patent grant is currently assigned to Norton Company. Invention is credited to David P. Gruber.
United States Patent |
4,474,585 |
Gruber |
October 2, 1984 |
Synthetic yarn-reinforced flexible webs stabilized against
elongation, coated abrasive thereon, and process therefor
Abstract
Conventional heat stretching and/or setting conditions for
fabrics made of heat sensitive thermoplastic yarns such as
polyester, and even special techniques advanced in prior patents,
have been found in adequate to produce coated abrasives with
sufficient elongation resistance for some very heavy duty service.
A superior alternative is provided by encasing the yarns in the
backing in a thermosetting adhesive and then curing it while
mechanically restraining the yarns from shrinking, as they would
under the temperature conditions employed for cure if no restraint
were used. The method is also applicable to other types of yarn
reinforced web materials for which a combination of elongation
resistance and flexibility is needed.
Inventors: |
Gruber; David P. (Scotia,
NY) |
Assignee: |
Norton Company (MA)
|
Family
ID: |
23986282 |
Appl.
No.: |
06/499,688 |
Filed: |
May 31, 1983 |
Current U.S.
Class: |
51/298; 427/171;
427/175; 427/381; 427/386; 427/389.9; 427/412; 428/102; 428/105;
428/109; 428/323; 442/73 |
Current CPC
Class: |
B24D
3/002 (20130101); B24D 11/00 (20130101); Y10T
442/2115 (20150401); Y10T 428/25 (20150115); Y10T
428/24091 (20150115); Y10T 428/24033 (20150115); Y10T
428/24058 (20150115) |
Current International
Class: |
B24D
3/00 (20060101); B24D 11/00 (20060101); C09K
003/14 () |
Field of
Search: |
;51/298
;428/257,240,323,102,105,109 ;427/171,175,386,381,389.9,412 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
45408 |
|
Feb 1982 |
|
EP |
|
73313 |
|
Mar 1983 |
|
EP |
|
Primary Examiner: Bell; James J.
Attorney, Agent or Firm: Chow; Frank S.
Claims
What is claimed is:
1. A web material characterized by the presence of at least one
reference direction for which the reference direction yarn set has
at least one half the total tensile strength of said web material
in said reference direction, said reference direction yarn set
additionally having a natural shrinkage value of at least 1%, said
web material having a free shrinkage of no more than 0.5% when
exposed to a temperature of 121.degree. C. for at least 10 minutes
without mechanical restraint.
2. A web according to claim 1, wherein the said reference yarn set
is predominantly a substantially coplanar and coparallel yarn
array.
3. A web according to claim 2, wherein said substantially coplanar
and coparallel yarn array is the warp or fill yarn array of a
coherent stitch bonded fabric.
4. A web according to claim 3, wherein at least half the yarns of
said substantially coplanar and coparallel yarn array are polyester
with a tenacity of at least 8 gm/denier.
5. A web according to claim 4, wherein said reference yarn set is
encased by a layer of material which is the product of the thermal
cure of a phenol-formaldehyde or resorcinol-formaldehyde resin or
of the radiation cure of multifunctional acrylates.
6. A web according to claim 3, wherein said reference yarn set is
encased by a layer of material which is the product of the thermal
cure of a phenol-formaldehyde or resorcinol-formaldehyde resin or
of the radiation cure of multifunctional acrylates.
7. A web according to claim 2, wherein said reference yarn set is
encased by a layer of material which is the product of the thermal
cure of a phenol-formaldehyde or resorcinol-formaldehyde resin or
of the radiation cure of multifunctional acrylates.
8. A web according to claim 1, wherein said reference yarn set is
encased by a layer of material which is the product of the thermal
cure of a phenol-formaldehyde or resorcinol-formaldehyde resin or
of the radiation cure of multifunctional acrylates.
9. A coated abrasive comprising abrasive grits adhered to at least
one major surface of a web material characterized by the presence
of at least one reference direction for which the reference
direction yarn set has at least one half the total tensile strength
of said coated abrasive in said reference direction, said reference
direction yarn set also having a natural shrinkage of at least 1%,
said coated abrasive having a maximum elongation of not more than
3.1% when subjected to cyclic elongation testing between 3.6 and
18.3 kN/m at 66.degree. C.
10. A coated abrasive according to claim 9, wherein the said
reference direction yarn set is predominantly a substantially
coplanar and coparallel yarn array.
11. A coated abrasive according to claim 10, wherein said
substantially coplanar and coparallel yarn array is the warp or
fill yarn array of a coherent stitch bonded fabric.
12. A coated abrasive according to claim 11, wherein at least half
the yarns of said substantially coplanar and coparallel yarn array
are polyester with a tenacity of at least 8 gm/denier.
13. A coated abrasive according to claim 12, wherein said reference
direction yarn set is encased by a layer of material which is the
product of the thermal cure of a phenol-formaldehyde or a
resorcinol-formaldehyde resin or of the radiation cure of
multifunctional acrylates.
14. A coated abrasive according to claim 11, wherein said reference
direction yarn set is encased by a layer of material which is the
product of the thermal cure of a phenol-formaldehyde or a
resorcinol-formaldehyde resin or of the radiation cure of
multifunctional acrylates.
15. A coated abrasive according to claim 10, wherein said reference
direction yarn set is encased by a layer of material which is the
product of the thermal cure of a phenol-formaldehyde or a
resorcinol-formaldehyde resin or of the radiation cure of
multifunctional acrylates.
16. A coated abrasive according to claim 9, wherein said reference
direction yarn set is encased by a layer of material which is the
product of the thermal cure of a phenol-formaldehyde or a
resorcinol-formaldehyde resin or of the radiation cure of
multifunctional acrylates.
17. A process for making a web material having at least one
reference direction in which the free shrinkage is no more than
0.5% upon exposure to a temperature of 121.degree. C. for at least
10 minutes from a reference direction yarn set which has a natural
shrinkage of at least 1% and at least half the total tensile
strength of said web material in said reference direction,
comprising the steps of:
(a) encasing said reference direction yarn set, together with any
adhesive impregnant or encasement previously applied to said
reference yarn set, within a mass of a stablizing adhesive capable
of cure to a solid state with a strain modulus and adhesion to the
yarns of said set sufficient to restrain the yarns of said
reference direction yarn set against more than 0.5% free shrinkage
when exposed to a temperature of 121.degree. C. for ten minutes;
and
(b) curing said stabilizing adhesive of part (a) while mechanically
restraining the yarns of said reference direction yarn set from any
shrinkage.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to webs or backings which are reinforced
with organic synthetic thermoplastic yarns, are ultimately utilized
in products requiring a combination of good elongation resistance
with sufficient flexibility to accommodate to repeated curving and
flexing, and are exposed to heat either in ultimate use or during
manufacture of the product in which they are ultimately used.
Examples of such products include conveyor and power transmission
belts, hoses, skirts for air supported vehicles such as marine
hovercraft, shells for air supported structures, and backings for
coated abrasives to be used in belt form. This invention is
particularly related to the latter group of products. The synthetic
yarns may be present in the webs as individual yarns or in the form
of fabrics. The invention is more particularly related to coated
abrasives reinforced in one of the manners described in U.S.
application Ser. No. 06/420,466 by Yarbrough, filed Sept. 20, 1982,
the specification of which is incorporated herein by reference.
2. Description of the Prior Art
Excessive stretch or elongation of backings which depend on
synthetic thermoplastic textile yarns for their primary strength
members has been a serious concern ever since these synthetic yarns
began to be used to replace cotton as reinforcing yarns. Various
expedients, primarily heat-stretching, have been used to ameliorate
the problem and are well known in the various arts in which the
problem has been encountered. With respect to coated abrasives,
some of the first practical means of reducing stretch were
described in U.S. Pat. Nos. 4,035,961 and 4,140,829 to Pemrick and
Cocanour. While the methods described in these patents were
substantial improvements over the prior art at the time and
provided products which are satisfactory for many applications of
coated abrasives, as evidenced by continuing commercial sales,
there are some applications for which the stretch resistance
achieved by these methods is not fully satisfactory.
A more recent development, which is especially useful in
combination with the methods of Pemrick and Cocanour and for
backings in which continuous filament synthetic yarns provide the
primary elongation resistance, is described in U.S application Ser.
No. 06/334, 710 by Ibrahim, now U.S. Pat. No. 4,396,657 and is
incorporated herein by reference. This Ibrahim method also advanced
the prior art but has proved not to be entirely satisfactory in all
cases. For applications requiring truly extraordinary stretch
resistance, especially when substantial heat is generated, still
further improvement is indicated.
Most workers in the prior art have relied on measurements at room
temperature to characterize the adequacy of elongation resistance,
and the most common measurement has been a conventional single
tensile test per web, backing, or product sample on a laboratory
tensile and elongation test machine. In part at least, this method
of testing has reflected a strong tendency in the prior art to
regard conventional heat setting and/or stretching as "permanently"
stabilizing yarns against shrinkage at any temperature
significantly lower than that of prior heat setting and/or
stretching.
SUMMARY OF THE INVENTION
It has now been discovered that a significant source of undesirable
elongation in backings comprising synthetic thermoplastic yarns as
their primary strength members is the shrinkage of such yarns
during exposure to heat, even after the yarns have been heat
stretched and/or set at higher temperatures. E.g., polyester yarns
set at more than 200.degree. C. still shrink significantly when
exposed to 121.degree. C., and such shrinkage drastically increases
susceptibility to elongation in later use. The shrinkage and the
elongation can both be reduced to levels lower than heretofore
achieved by restraining the yarns with sufficient force during all
stages of manufacture when the yarns are exposed to heat. In
backings or products which have continuous yarns extending
throughout the entire object or a substantial portion thereof, the
restraint can be provided by direct mechanical means. It has now
been found possible, however, and is normally more convenient, to
achieve the restraint by impregnating and/or encasing the yarns at
an early stage of manufacture with an adhesive which is capable of
curing to give a solid of high modulus and by curing the adhesive
sufficiently to obtain such a modulus while preventing shrinkage
via mechanical restraint. If the attachment of the warp yarns to
this encasing and/or impregnating adhesive is sufficient, the yarns
will not be able to shrink in subsequent processing steps because
of the restraint imposed by the adhesive. It is thereby possible to
achieve very low elongation while using the final product even
under conditions which generate considerable heat, without the need
for gross mechanical restraint against yarn shrinkages at the later
stages of manufacture, where such restraint may be particularly
inconvenient or expensive to supply.
In quantitative terms, I have found that yarns and fabrics with
over 1% free shrinkage at 121.degree. C. can be stabilized in this
manner so that the free shrinkage is reduced to 0.5% or less at the
same temperature, and that coated abrasives can be made so that
they will have a maximum elongation of 3.1% or less when repeatedly
cycled between tensile loads of 3.6 and 18.3 kilonewtons per meter
(kN/m) of width at a temperature of 66.degree. C. Coated abrasives
which meet this criterion have been found to give superior
performance in elongation-prone applications, even though their
elongation behavior when tested at room temperature was
indistinguishable from that of less effective conventional coated
abrasives.
If a fabric or other collection of yarns has less than 1% natural
free shrinkage at the highest temperature to which it is to be
exposed, no stabilization in the manner of this invention is
normally needed. E.g., for coated abrasives with conventional
phenolic resin maker and size adhesives, a temperature of
121.degree. C. is normally the maximum used in cure, and if a
fabric shrinks less than 1% at this temperature, there is little
need to stabilize it. Furthermore, if the yarns reinforcing a web
or product supply less than half the tensile strength of the web or
product in any direction, the instant invention is also not
normally valuable for that product.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention is particularly suitable for use with yarn
reinforced coated abrasive backings as described in Ser. No.
06/420, 466. In such backings normally all the warp yarns are on
one side of the backing, and thus can conveniently be encased
and/or impregnated with an adhesive without substantially
impregnating the other yarns in the backing at the same time. The
side with the warp direction yarns can conveniently be made the
back of the eventual coated abrasive product, so that the cure of
the adhesive needed to stabilize the warp yarns against shrinkage
does not necessarily entail extensively exposing such a cured
adhesive on the side of the product to be coated with abrasive
grits. It is well known in the art that inferior grits adhesion can
be the result of excessively advancing the cure of any adhesive
used on the front side of the backing before the maker adhesive,
which is to hold the grits, is applied. When the warp yarns, which
are the principal determinants of elongation resistance, are
segregated on the back side of the backing web, a substantially
advanced resin adhesive encasing and/or impregnating them can be
combined with a very slightly advanced resin on the front side of
the backing to maintain receptivity to forming a strong bond with
the maker adhesive coat to be applied later. Such a combination of
the instant invention with that disclosed in application Ser. No.
06/420,466 is highly preferred.
It is preferred that the yarns which are to lie in the stretch
resisting direction in a final coated abrasive product should form
a substantially coplanar and coparallel array as described in the
Yarbrough Application cited above. Most preferable is the
embodiment in which all such yarns form a single array which is
disposed on one side of all the other reinforcing yarn arrays in
the backing, and in which the stretch resisting yarns are disposed
on the opposite side from the abrasive grits coating in the final
product. Several fabrics highly suitable for use in this way are
described in U.S. application Ser. No. 06/297,538 by Darjee, which
application is incorporated herein by reference.
While thermoplastic textile yarns of almost any type may be used
with the instant invention, yarns of the common and economical
synthetic yarns such as polyester, polyamide, and polyacrylonitrile
are preferred. Particularly preferred, primarily because of their
relatively low cost per unit tensile strength, are continuous
multifilament high tenacity polyester yarns in deniers from 840 to
2600.
The most straightforward way of achieving the desirable products of
this invention is to carry out every step of the manufacture of a
backing and a coated abrasive coated thereon while maintaining a
tensile force on the backing sufficient to prevent any lengthwise
shrinkage during any process in which heat is applied to the
backing. However, this procedure is not normally preferred in
practice, because existing commercial equipment for drying and/or
cure of adhesives in the making and grits sizing stages is not
provided with the necessary mechanical means to achieve such
restraint. Accordingly, it is normally preferred, for reasons of
economy, to achieve the stabilization of warp yarns against
elongation by encasing and/or impregnating these yarns at a fairly
early stage of cloth finishing with an adhesive which can be cured
to a solid with sufficiently high modulus and sufficently good
adhesion to the yarns to restrain them from elongation in
subsequent use. Part of this restraint against ultimate elongation,
as already noted, is achieved by restraining the yarns against free
shrinkage that could otherwise occur in later stages of
manufacturing. Such an adhesive is described herein as a
stabilizing adhesive.
Suitable stabilizing adhesives are normally thermosetting resins,
in order to achieve a high modulus which is not severely reduced by
exposure to heat. The adhesives must also form strong bonds with
the yarns to be stabilized, or with some other adhesive which is
applied to these yarns first for other purposes, e. g.,
supplemental stabilization and fray resistance as described in the
Ibrahim application cited above. Polyimides, suitably formulated
urethanes, radiation curable acrylates, etc. are all suitable. For
most coated abrasive uses, resorcinol- and/or phenol-formaldehyde
resins are preferred, for economy and compatibility with the usual
phenol-formaldehyde maker and sizing resins for such products. As a
matter of processing convenience and economy, rapidly curable
adhesives are preferred, and for this reason resins which contain
some organic solvent are often preferred over those which are
purely water based, because the latter are more likely to blister
when rapidly dried.
In order to measure and define the adequacy of the stabilization
achieved, it is convenient to have a laboratory test method,
although the ultimate criterion of success must be adequate
performance in actual applications of coated abrasives to practical
use. It has been found that a good correlation is obtained between
belt performance in elongation-prone use and laboratory measurement
of elongation under cyclic loading between two tensile forces at a
temperature of 66.degree. C.
For this test, an Instron tester was used, with a sample of backing
or coated abrasive product 2.5 cm in width and an initial jaw
opening of 25.4 cm at zero tensile force. The sample was
equilibrated at the test temperature and then subjected to
extension at a rate of 2.5 cm/min until a force of the chosen upper
limit was registered. At this point, the jaws reversed direction
and closed at the same rate until the tensile force was reduced to
the chosen lower limit. This cycling was automatically continued,
with continuous recording of the jaw spacing and tensile force,
until several cycles had given the same jaw spacings for each value
of tensile force. The tensile force was then returned to zero. The
maximum elongation reached in the first cycle was denoted as A and
the maximum elongation in the final cycle(s) was denoted B. The
difference between the initial and final lengths for zero tension
was recorded, as a percent of the initial length, as the permanent
deformation, denoted C. It was found that C was always positive and
that B was always larger than A. The most important correlation
with practical performance was found to be with elongation B: if
that value in a final coated abrasive product was 3.1% or less in
cycling between 3.6 and 18.3 kN/m at 66.degree. C., satisfactory
stretch resistance even in demanding applications was found.
It should be noted that the description above has been given in
terms of stabilization of warp yarns, simply because these yarns in
the fabric as manufactured most often become the principal
elongation resisting yarns in the coated abrasive belts as used. It
is, however, also well known in the art to make sectional belts for
applications demanding greater belt width than is available in
coated abrasive webs from many commercial makers. In such cases,
the elongation resistance of the final belts is more dependent on
the yarns in the fill rather than the warp direction of the
original fabric backing used. For coated abrasives to be used in
this fashion, the fill rather than the warp yarns should be
stabilized. In general, the Yarbrough application and certain other
prior art teach the possibility of more than two arrays of yarns
oriented in various directions in the backing, and all the yarns
which will lie in or near to the direction in which maximum stretch
resistance of the final belt is desired should preferably be
stabilized as described herein.
Furthermore, although the preferred embodiments have been described
principally in terms of backings suitable for coated abrasives, it
is clear that very similar applications can be made to other
fields. Webs for air-supported structures, e.g., normally need
stretch resistance approximately equal in all directions in the
plane of the backing. For such a use, a web should have all its
yarns stabilized by the methods described herein. (For such an
application, normally no additional coating on one surface only is
needed as for coated abrasives, so that the possibility of reduced
adhesion of such a coating is of no practical consequence.) A web
for conveyor belts, on the other hand, is more like one for coated
abrasives in that elongation resistance in one direction is
normally much more important than in other directions.
The benefits and application of the instant invention are further
illustrated by the following examples.
EXAMPLE 1
A stitch bonded fabric consisting of 14 warp yarns of 1300 denier
high tenacity multifilament polyester per 25 mm of fabric width, 96
fill yarns of 170 denier texturized multifilament polyester per 25
mm of fabric length, and stitch yarns of 140 denier high tenacity
polyester was used as the substrate for this example. Further
details of the construction and method of manufacture of this type
of fabric are given in the Darjee application cited above.
This fabric was first saturated with an epoxy resin emulsion and an
imidazole curing agent to extent of 67 dry gm/m.sup.2. Details of
preferable resin compositions and methods of saturation are given
in the Ibrahim application cited above. The fabric was then ready
for the stabilization process according to this invention.
The stabilizing adhesive used was a mixture of Resinox 7451, a
phenolic laminating resin in methanol supplied by Monsanto Co., St.
Louis, MO 63166, 30 parts by weight; finely ground calcium
carbonate, 40 parts by weight; and paraformaldehyde, 3 parts by
weight. This mixture was applied to the warp yarn side of the
saturated fabric by knife coating so as to give a layer with a dry
add-on weight of 118-148 gm/m.sup.2 thoroughly encasing the warp
yarns. The applied adhesive was then subjected to cure under
various time and temperature programs as shown in Table 1 below.
During the cure, the samples were kept under a tensile force of
more than 3 kN/m to prevent free shrinkage.
Because of cooling of the oven when it is opened to admit the
samples, evaporation of solvents, and other factors, it is
generally suspected that the actual temperature attained by the
backing when curing samples for such short times as these is not as
high as the nominal oven temperature. Therefore, a set of
temperature recording appliques (available from Telatemp Corp.,
Fullerton, Calif.), was affixed to each sample. These are capable
of measuring the maximum temperature attained at their surface
within three degrees Celsius. The temperature of the highest
changed applique is shown as the "Actual Backing Temperature" in
the Table.
For each time and temperature program shown in the Table, there are
two entries for each of the three elongation numbers already
defined. The first set of these entries is for backing samples
which were subjected to the cycling testing without further
exposure to heat above room temperature between the cure and the
cyclic testing. The second set of entries is for samples which were
allowed to shrink freely under ten minutes exposure to 121.degree.
C. between cure and testing.
The results in the Table clearly show the deleterious effect of
free shrinkage on elongation resistance, along with the reduction
of this deleterious effect effected by greater degrees of cure of
the stablizing adhesive. Either five minutes at a backing
temperature of 177.degree. C. or two to four minutes at 188.degree.
C. yields backings with no more than 0.5% free shrinkage in the
test shown.
TABLE 1 ______________________________________ Effect of Extent of
Cure of Stabilizing Adhesive on Backing Shrinkage Susceptibility
and Elongation Resistance Cure Conditions Percent Actual Elongation
Oven Tem- Backing Percent and Defor- perature, Exposure Tempera-
Free mation:.sup.1 .degree.C. Time, Min ture, .degree.C.
Shrinkage.sup.2 A B C ______________________________________ No
Stabilizing Adhesive Used -- 3.7 3.9 1.3 " 1.2 5.6 5.7 3.0 191 2
163 -- 2.3 2.5 0.5 " " " 2.4 5.1 5.3 3.0 204 2 177 -- 2.1 2.3 0.6 "
" " 2.1 4.5 4.8 2.7 204 5 177 -- 1.7 1.8 0.4 " " " 0.5 2.2 2.5 0.7
224 2 188 -- 2.1 2.3 0.6 " " " 0.4 2.9 3.2 1.6 224 3 188 -- 1.9 2.1
0.7 " " " 0.5 2.4 2.7 0.9 224 4 188 -- 1.7 1.9 0.4 " " " 0.2 2.3
2.5 0.7 ______________________________________ .sup.1 During
cycling between tensions of 3.6 and 18.3 kN/m at 66.degree. C.; the
designations A, B, and C are explained above. .sup.2 Upon exposure
to 121.degree. C. for 10 minutes without mechanical restraint.
Some of the most elongation backings shown in Table 1 were then
further processed to make coated abrasives by the processes shown
in detail in the Ibrahim application already cited. These processes
entail heating at 100.degree. C. or more for many hours in order to
achieve full cure of the phenol-formaldehyde maker and sizer resin
adhesives used. When such cure was performed without any restraint
against shrinkage, the resulting coated abrasives had at best 3.8%
B value elongation. While a considerable improvement over results
achieved for otherwise similar products without any stablizing
adhesive, this level of elongation resistance is still not entirely
satisfactory for all coated abrasives.
If one of these stablized backings, or indeed almost any other
coated abrasive backing with a considerable amount of thermosetting
resin encasing and/or impregnating the yarns, was converted to a
coated abrasive while under sufficient tensile force to prevent
free shrinkage at any stage of processing, fully satisfactory
elongation resistance wss achieved. However, it was usually not
achieved until the final cure after making, sizing, and preliminary
sizer cure, and as already stated above, maintaining a coated
abrasive under tension during the late stages of cure is generally
impractical in large-scale manufacturing.
(End of Example 1)
The results shown in Example 1 indicated the general direction of
changes to be made to achieve satisfactory stabilization at an
early stage of commercial scale manufacture. Such a result is shown
in Example 2.
EXAMPLE 2
For this example, a stitch bonded fabric consisting of 14 warp
yarns of 1300 denier high tenacity polyester per 25 mm of fabric
width, 128 fill yarns of 150 denier texturized polyester per 25 mm
of fabric length, and 70 denier high tenacitY polyester stitch
yarns was used. Again, details of the construction of this fabric
are given in the above cited Darjee Application.
This fabric was saturated in the same manner as for Example 1, with
the important exception that the fabric was stretched 2.5-3% of its
original length in the tenter frame before drying. The stabilizing
adhesive was the same as in Example 1, except that hexamethylene
tetraamine was substituted for the paraformaldehyde. (Any
formaldehyde donor is considered equivalent for use in this
formula.) In contrast to Example 1, the stabilizing adhesive for
this example was dried in a continuous oven, so that the backing
reached actual oven temperatures, which were 121.degree. C. for two
minutes followed by 204.degree. C. for one minute. As in Example 1,
the cure of the stabilizing adhesive was accomplished while the web
was under restraint in the warp direction, so that no shrinkage of
the warp yarns could occur. The amount of stabilizing adhesive was
the same as in Example 1. After completion of the stabilizing
process, the backings were given a frontfill, another backfill, and
then made into coated abrasives with phenolic resin maker and size
adhesives in the manner described in detail in the Ibrahim
Application cited above.
The elongation results for products made in this way are shown in
Table 2 and compared with those achieved by proceeding according to
the original Ibrahim directions. It is clear from the Table that
the stabilizing adhesive has considerably improved the elongation
resistance as measured by cyclic testing of heated samples.
The superior quality of coated abrasives prepared according to this
Example was confirmed by field testing in grinding of 40-50 pound
grade industrial particleboard about 125 cm in width, using a
Kimwood Serial 50145 machine with 125 horsepower driving motor and
a steel contact roll about 250 cm in diameter. The particle board
was passed through the grinding nip at a rate between 25 and 35
meters per minute. Performance with the belts of coated abrasives
according to this Example averaged at least 25% greater than when
conventional products were used.
(End of Example 2)
EXAMPLE 3
The saturation adhesive and process for this example were identical
to that for Example 2. However, the backfill adhesive described in
the Ibrahim Application was used in this Example as the stabilizing
adhesive. It was applied as in the cited Application, but was cured
under tensile restraint for two hours at 113.degree. C. rather than
for only a few minutes as described by Ibrahim. Subsequent
processing steps proceeded as described by Ibrahim. An elongation B
value of 2.5% in cyclic testing between 3.6 and 18.3 kN/m at
66.degree. C. was obtained.
TABLE 2 ______________________________________ Effect of Stretch
During Saturation and Stabilizing Adhesive on Elongation Resistance
of Coated Abrasives Cyclically Tested with Various Upper Load
Limits Upper Percent Elongation Limit and Deformation Test at
66.degree. C. When Load, Cycled from 3.6 kN/m Product
Type/Description kN/m A B C ______________________________________
Grit 120 Closed Coat SiC 12.8 1.4 2.0 0.5 on backing prepared
accord- 14.6 2.2 2.6 0.8 ing to 06/334,710 16.4 2.9 3.4 1.3 18.3
4.0 4.4 1.9 Grit 100 Closed Coat SiC 12.8 0.9 1.2 0.2 Cloth on
Stabilized 14.6 1.2 1.5 0.3 Backing, Otherwise as Above 16.4 1.5
2.0 0.4 18.3 2.3 3.1 1.6 Grit 36 Open Coat NorZon.sup.1 Cloth on
Backing Accord- 18.3 4.5 5.1 2.7 ing to 06/334,710 Grit 36 Open
Coat NorZon.sup.1 Cloth with Stablization Replacing Backfill of
18.3 2.2 2.7 0.9 Item Above Grit 36 Open Coat NorZon.sup.1 Cloth
with Stabilization plus all other finishing 18.3 1.5 2.0 0.6
treatments of 06/334,710 ______________________________________
.sup.1 Trade mark of Norton Company for products coated with
zirconiaalumina grits.
(End of Example 3)
EXAMPLE 4
This example is the same as Example 3, except for the stabilization
stage. The stabilizing adhesive was a mixture of Uvithane 783 from
Thiokol Chemical, 572 parts; pentaerythritoltriacrylate, 572 parts;
Celrad 3700 from Celanese Chemical, 572 parts; N-vinyl pyrrolidone,
484 parts; Irgacure 651 from Ciba-Geigy, 100 parts; Tyzor TBT from
DuPont Chemical, 60 parts; fumed silica, 50 parts; and silica in
about 1000 mesh size, 3000 parts; all parts are by weight.
(Uvithane and Celrad are acrylate oligomers, Irgacure is a
photo-initiator, and Tyzor is an organotitanate adhesion promoter.)
A mass, essentially the same both dry and wet, of 170-190
gm/m.sup.2 of this adhesive was applied to the warp yarn side of
the saturated fabric and then cured by two minutes exposure to
ultraviolet light while the fabric was held in a pin frame, so that
it could not shrink. Coated abrasive products with elongation B
values of 2.7% in cyclic testing between 3.6 and 18.3 kN/m at
66.degree. C. were obtained.
(End of Example 4)
In order to describe precisely the instant invention, it is useful
to define certain additional special terms. A particular direction
defined by a straight line lying in the plane of a web is denoted
as a "reference direction". All the yarns in the web whose
direction is within 45.degree. of the reference direction are
denoted together as the "reference direction yarn set". The amount
of shrinkage which the yarns of any set would exhibit when exposed
for at least ten minutes to a temperature of 121.degree. C., in
isolation from all other components of the backing and free from
mechanical restraint, is denoted as the "natural shrinkage". If the
yarns are present in the backing as part of a fabric, their
shrinkage according to this criterion would be measured on the
isolated fabric, not on separated yarns. Although the natural
shrinkage can not usually be measured directly when the yarns of
the reference direction yarn set are embedded in a composite
structure, this value can be determined from knowledge of the fiber
type, number, and size of the yarns in the set. If several
different variations of the general fiber type or types found in
the structure are commercially available and have significantly
different shrinkage characteristics, the value for yarns of the
highest tenacity variation is to be assumed.
* * * * *